Magically changing values in JS object

I dont know how to describe this better but I have never seen a behaviour like this. 😀

I have a JS object emospro with an attribute emospro.billing which is an array with four values.

I filled the object with some data and then checked it like this:

console.log(emospro.billing);
console.log(emospro);
console.log(emospro.billing);

The reason for this construction is that the results a strange.

The first log gave me this:

['1000000635', 'not_set', 'be/STADT/0000', 247.81]

which is what I expected. The third log gave me the same:
['1000000635', 'not_set', 'be/STADT/0000', 247.81]

So far so good. But then the second log with the whole emospro-Object returned this:

{
    "billing": [
        "u3f_3g8hEOuyhiyF*VAnxS4bQoLVQHXW9feqghZKHWo",
        null,
        null,
        247.81
    ]
}

It encrypted/hashed somehow the first value, nulled the second and third and only the last value is correct. I altered the last value by myself to check if it is reacting and it does. On the first three values I have no influence in the second log.

How is this even possible without influencing the log before or after??

I am confused. Somebody with an idea?